UPDATE: I ran into an issue with step 8 of Patrick's steps. I recently realized this numbering was not working correctly in a form I created when I tried to replicate these steps in a new form. My former form numbering appeared to be working only because the default view is being sorted by ID in descending order. According to Patrick, this method is supposed to select the active form being submitted which naturally would be the next max ID (but it should not pick the physical top ID in the list) and therefore it shouldn't matter what the View's sort order is. To correct this, a clarification should be inserted after step 8:
"8. Add another action that sets the ID in your main data source
equal to the ID column returned from the data section of your FormQuery
secondary data source - that's the current max ID. "
Clarification:
8.1 Filter on @ID from
secondary source FormQuery. Step 8 Add Action should look similar to this: Set a field’s value: LibID = @ID[@key = key]
p.s. Maybe that's what you mean in step 8, but it obviously was not clear to me so it may not be clear to others. HTH.